高应力条件下的岩芯电磁性能变化

黄启文; 李阿伟

doi:10.12090/j.issn.1006-6616.2019.25.04.042

STRESS INDUCED CHANGES IN THE ELECTRICAL-MAGNETIC PROPERTIES OF ROCK CORESHUANG

doi: 10.12090/j.issn.1006-6616.2019.25.04.042

HUANG Qiwen^1
,,
LI Awei²

1.
J. S. Lee Memorial Museum, Beijing 100081, China
2.
Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China

摘要

Abstract: The Standard Lattice Model predicts that under high stress, the outer most electrons of the Si-O bonds of a rock get ejected into the lattice's interstitial space. This loosely bound exoelectron cloud will, in a battery's electric field, have a direct current (DC) I; it will also absorb electromagnetic (EM) waves which result in an alternating current (AC) component in the induced current. Both effects have been measured. At high stress just before fracture, the DC current shows a slow rise due to electron tunneling followed by a sudden rise due to the breaking bond electrons. The AC current's voltage amplitude shows a drop as the current increases, and returns to normal after fracture when the current decreases to normal. This is the conservation of energy:absorbed wave energy E=V×I, AC current power. This AC fracture result demonstrates that EM waves can be used to actively probe the changes in highly stressed crust zones.
- Standard Lattice Model /
- exoelectron cloud /
- electron tunneling /
- breaking bond /
- electromagnetic wave /
- direct current /
- alternating current /
- absorbed energy /
- conservation of energy
摘要: 根据标准晶格模型理论，在高应力作用下，岩石的Si-O键最外层电子将被挤入晶格间隙里，松散外逸的电子云在电场中将产生直流电流（DC），进而吸收电磁波，转换成交流电流（AC）。直流电流来源于量子力学穿隧效应电子和断键电子。穿隧效应电子的形成过程和原理：氧原子的最外电子被束缚在浅位能井（shallow potential well）（0.38 V），当高应力作用时，电子吸收部分能量，增加其动能，虽然这种轻微的动能增加不足以使电子克服并跳出它的位能井（potential well），但它足以增加穿过井壁（well wall）进入晶格空隙间的概率，这个概率乘以可用氧原子的数目即为由于隧穿效应形成电子云的电子数量，其量级通常为微微库伦（picocoulombs）到纳米库伦（nanocoulombs）。断键电子的形成过程和原理：从微裂纹开始断裂键释放电子，并且裂纹成核点极可能开始是平行排列的，每当Si-O键断裂时，就会产生一个+Si悬键，伴随着一个自由电子附着在-O原子上，这个电子将从原子跃迁到原子，这种电子电流与裂纹的表面积和电池电极的收集效率成正比。断键形成的电子云比穿隧效应多很多。两种电子均被试验所证实。在高应力条件下岩石破裂之前，由电子穿隧效应，DC缓慢增加，随着岩石破裂的发生而导致断键电子增多，DC急剧增加；AC的电压振幅（V）随电流（I）增大而减小，当电流减小到正常时，在岩石破裂后电压振幅回归正常；遵守能量守恒原理，吸收的电磁波能量（E）与交流电流功率（V×I）相等，即E=V×I。研究结果表明电磁波监测可用于探测地壳高应力变化和岩石破裂特征，当应力达到岩体断裂的临界强度时，其应变晶体结构开始释放越来越多的外逸电子，最终岩体晶体结构断裂产生一个地震或滑动事件。岩石破裂的电磁性能变化研究可用于研发电磁波地学监测仪器，电磁波监测可以作为地应力监测的一种补充和对比分析方法，两种方法相结合比地应力监测一种方法更可靠。此外，在高应力条件下岩石还有其它现象：应变蠕变辐射、光发射、声发射、静电等，这些现象的观测也是预测地质事件需要考虑的条件。
- 晶格模型 /
- 外电子云 /
- 量子穿隧效应 /
- 断键 /
- 电磁波 /
- 直流电 /
- 交流电 /
- 吸收能量 /
- 能量守恒
注释:

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注释:

图 1 石英晶格结构(外溢电子挤入原子间空隙，绿圈代表Si, 红圈代表O)

Figure 1. Quartz lattice structure, interstitial space between atoms where exoelectrons can move in

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图 2 实验装置(220吨压力机、25 mm×50 mm圆柱型样品、电压表、示波器、电池串联电路和50 Hz背景辐射)

Figure 2. Experimental setup (200 ton press, with the sample (25 mm×50 mm cylinder), voltmeter, oscilloscope, and battery in a series circuit, and 50 Hz background radiation)

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图 3 花岗岩电压随应力/时间变化的曲线

Figure 3. Voltage vs Stress/Time, granite sample

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图 4 玄武岩电压随应力/时间变化的曲线

Figure 4. Voltage vs Stress/Time, basalt sample

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图 5 示波器显示照片

Figure 5. Screen photo

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图 6 不同时间下50Hz FT波峰

Figure 6. 50 Hz FT peak at different times

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